Electronic equipment using semiconductor devices are essential for many modern applications. Semiconductor image sensors are commonly involved in electronic equipment used for sensing light. Complementary metal-oxide-semiconductor (CMOS) image sensors are widely used in various applications, such as digital camera and mobile phone cameras. The CMOS image sensor typically includes an array of picture elements (pixels). Each pixel includes a transistor, a capacitor and a photo-diode. An electrical energy is induced in the photo-diode upon exposure to the light. Each pixel generates electrons proportional to an amount of light falling on the pixel. The electrons are converted into a voltage signal in the pixel and further transformed into digital signal.
The CMOS image sensors are classified as front side illuminated (FSI) image sensors and back side illuminated (BSI) image sensors, depending on the light path difference. The BSI image sensors are gaining in popularity. The light is incident on a back side of a substrate of the BSI image sensor and hits the photo-diode directly without obstruction from dielectric layers and interconnect layers formed on the substrate. Such a direct incidence makes the BSI image sensor more sensitive to the light.
However, as technologies evolve, the image sensor device is becoming increasingly smaller in size while having greater functionality and greater amounts of integrated circuitry. The BSI image sensor has been shrunk to a smaller pixel pitch and thus leads to undesirable performance of the BSI image sensor. Therefore, there is a continuous need to improve a structure and a manufacturing method for of the BSI image sensor device in order to improve the performance of the BSI image sensor device (e.g. increase quantum efficiency and full well capacity) as well as reduce cost and time on processing the BSI image sensor.